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Old 5th October 2004, 08:22 PM   #1
extremy is offline extremy  United States
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Default THX certification, or integrated near THX Quality,

Here's something I want to ask for feedback on.

From researching tube preamps and amps, I haven't found mention of an nice integrated 6.1 with Sub out.

Much less, once I begin looking at the higher quality formats in reproduction I never see tube equipment listed. Is this because there are no measurements for tubes?

If I ever go tube, I'd like to find a schematic for an integrated preamp/amp at least 6 channel, including surround, a center channel, and a sub channel. I'd rather see one huge unit for all my sound than ten or so separates. I'd get excited about tubes if I could get this accomplished. It would be much the same as an AV unit today. What could be more would be to understand how to incorporate controlling video from and to many separate feeds in the AV unit too.

If anyone wants to talk about this concept, or if anyone has researched this out, please feel free to join in. Any ideas are welcome. Since I haven't read across this topic I thought I'd add it in and see how much interest there is.

This forum is the best!!!
Hang in there,
Greg
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Old 5th October 2004, 08:50 PM   #2
Wodgy is offline Wodgy  United States
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You can do a six channel tube preamp easily. Nothing special here. Alps makes a six channel version of their "Blue" potentiometer. Just build a six channel preamp and away you go. There are some commercial solutions too, e.g. Mapletree Audio Design (though they use three stereo potentiometers, which seems annoying to me; if you bought a six-channel potentiometer yourself and sent it to Dr. Peppard I suspect he would build you a custom version).

A six channel integrated amp seems cost-prohibitive. For HT use, you'd want a push-pull design, so you'd be needing at least twelve power tubes, around twelve front end/phase splitter tubes, and a large amount of money for transformers. The chassis would have to be a huge multi-level affair.

I'd go with a tube preamp and some nice solid-state amps.
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Old 5th October 2004, 09:08 PM   #3
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One thing is the size of the tubes. They're gigantic compared to the chips used in 99.999999% of the AV gear. It's perfectly possible to make simple single-tube preamp circuits so the preamp box wouldn't be that large. The poweramp would be pretty huge though. But I don't think that's the main reason for so few tube AV stuff.
I think many designers think about all the SS stuff the signals go thru in such components that using tubes is kinda a waste. Even all the filters and attenuation is done inside the chips.
Imagine a high-end fully balanced tubed AV system with all filters being passive and all channel's volumes handled by balanced precision stepped ladder attenuators. we're talking some serious money here!
Another thing is that most people think they need hundreds of watts in each channel for AV to be any good, and now we're really talking humungus!
Of course if all speakers were really efficient, like large horns, a low wattage SE triode system would work great. But not only are such speakers increadibly expencive, but also very large. So you'd need a huge room to place this hobby into, and that means a big rich-persons home, and therefore very few customers.
I dunno, but that most be some of the reasons.
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Old 6th October 2004, 02:16 PM   #4
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Most of the objections are size and costs. But it is very do-able. If you have the $.

But first my pet peeve. THX certification means zip. There ...I've said it.

Here is my proposal John Swenson BDT preamp (1 pot does 6 channels volume control) the .1 channel has a little phase switch for the subwoofer. (Your only feature apart from volume control)

Subwoofer is active...ie. SS.

Then build 5 Single ended 2a3/300b amps..say paramour by bottlehead
Get 5 channels of efficient loudspeakers.

Voila.

Cheers,
Bas
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Old 6th October 2004, 06:04 PM   #5
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Compactrons with a (modern) Matrix topology for preamplifier operation might do okay, compact size and all...

Btw. THX is bull

A power amplifier doesn't need to be large either to sound great and blow away all the other amps out there...

Think of PP 813's?, 200w/ch (can go higher), coupled with a nice preamp tube and you're away, could do it with a relativley small power supply and chassis too...

If you're after SE, there are a couple of circuits with 45w and 66w RMS respectivley:
http://members.aol.com/analogengineer/813mat.htm
http://www.pmillett.addr.com/813_se_triode_amps.htm
http://homepages.ihug.co.nz/~rwillis/

A stackable 2U frame for your 6 channels is doable, and provides excellent ventilation, be prepared to store it in a seperate room though if you're going to use fans to cool.

I should think you could get away with a dual 120mm fan ontop of a rackmount cabinet and have every 2U case with passive ventilation on top and bottom, lets the heat passthrough to the second (ontop-unit) and so forth.

Be prepared to design well though!

Quote:
What could be more would be to understand how to incorporate controlling video from and to many separate feeds in the AV unit too.
A well filtered 12v power supply, a couple of relays, point-to-point shielded 75ohm cable (minature shielded), star-grounding, maybe even the ability to prevent ground loops via 1:1 trafos could be incproperated all into a single 1U rackmount cabinet, yup thats pretty much all you need...

Cheers! (Last edit)
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